Gibbs' adsorption at α alumina–copper interfaces

Abstract

Gibbs adsorption isotherms of oxygen to α alumina–transition metal interfaces are derived from a point defect model that handles chemical interactions and crystallographic structure at the interface. The model considers structural vacancies and interfacial charge transfer clusters as characteristic interfacial point defects. Majority defect type and concentrations strongly depend on the oxygen activity. Adsorption isotherms are derived for typical data sets for liquid and for solid copper in contact with alumina, revealing three adsorption ranges: adsorption-free interfaces in an intermediate oxygen activity range, interfaces with oxygen excess in form of interfacial oxide charge transfer clusters at high oxygen activity and oxygen deficient interfaces with interfacial metal clusters at low oxygen activity. The model predicts differences in adsorption behavior for crystallographically different interfaces; “polarity” and atom density in the interfacial oxide plane play key roles. Model predictions are confronted to literature results on the wetting behavior of alumina by liquid copper and to EELS investigations on the interfacial bonding in the solid Cu–alumina system.